The human body is host to a highly complex and rich microbial community. These microorganisms are generally harmless and contribute to a healthy state by producing vitamins, cooperating with digesting food, or stimulating the immune system. The human microbiota mainly resides on the surface and in deep layers of skin, in the saliva and oral mucosa, in the conjunctiva, and in the gastrointestinal tracts.
It has been demonstrated, primarily in the gut, that human microbiota have fundamental roles in human health and disease. The skin is colonized by a large number of microorganisms, most of them are beneficial or harmless. However, the skin microbiome has specific compositions in diseases states of skin that are different compared to healthy skin. Diseases such as acne vulgaris are associated with strong alterations of the microbiome.